Nectar sugar content: estimating standing crop and secretion rate in the field

Field techniques for sampling and measuring the standing crop and secretion rate of nectar are described, in order to clarify some discrepancies and omissions in existing reviews of nectar measuring techniques. Slender microcapillary tubes (a fresh one for each sample) are recommended for withdrawing nectar, and a hand held sucrose refractometer, capable of operating with very small fluid volumes, is used for measuring concentration. Potential errors due to the presence of solutes other than sucrose, or to temperatures other than the calibration temperature, are discussed. I consider how measurements of secretion rate are affected by reabsorption and by the nature of the bags used to exclude nectarivores.